Ethylene-α-olefin copolymers such as an ethylene-propylene bipolymer (hereinafter abbreviated as EPM) and ethylene-propylene-nonconjugated diene terpolymer (hereinafter abbreviated as EPDM) are excellent in moldability, mechanical properties, water resistance, weatherability, heat resistance and chemical resistance, and are therefore being used in many fields of, for example, car components, home electric appliances and office equipment. In addition, since thermoplastic elastomers obtained by blending an ethylene-α-olefin copolymer and polyolefin resin such as polypropylene and polyethylene have excellent properties and recyclability, they are now attracting attention mainly in terms of applications to automobiles.
However, ethylene-α-olefin copolymers and the aforementioned thermoplastic elastomers have a defect that because they do not have a polar functional group in the molecule, their affinity with other substances is poor, and thus the coatability and the adhesiveness are quite inferior.
To overcome the above defect, an attempt to introduce a hydroxyl group, which is a polar functional group, into the structure of an ethylene-α-olefin copolymer, that is, to modify the ethylene-α-olefin copolymer with hydroxyl groups, has been variously studied. For example, a method comprising epoxidizing a double bond in EPDM using hydrogen peroxide and then conducting hydrolysis has been disclosed (e.g., see Patent Document 1). Furthermore, a method of grafting in which a vinyl monomer having a hydroxyl group, such as 2-hydroxyethyl methacrylate, is reacted with a mixture of EPM and polypropylene in the presence of a radical generator such as dialkyl peroxide has been proposed (e.g., see Patent Document 2).
[Patent Document 1] Japanese Patent Laid-Open Publication No. 9-241448 (p.7)
[Patent Document 2] Japanese Patent Laid-Open Publication No. 3-258845 (pp.4 to 5)
However, the method described in Patent Document 1 is a two-stage process, which also requires use of a great amount of organic solvent such as toluene to dissolve EPDM, and the method was thus complex and economically disadvantageous. In addition, the method had an essential problem that it cannot be applied to ethylene-α-olefin copolymers which do not contain a double bond.
In addition, the method described in Patent Document 2 had a problem that because polymer radicals produced by a radical generator such as dialkyl peroxide react with each other to be cross-linked, or suffer from decomposition before reacting with a vinyl monomer to cross-link or degrade the resin, thereby damaging the processability and the properties of the resin. Further, because of occurrence of homopolymerization of vinyl monomers or loss of ester moieties to which a hydroxyl group is bonded caused by hydrolysis, it was also difficult to introduce a hydroxyl group efficiently.